Heating apparatus



Sept. 28, 1965 J. D. NESBITT ETAL HEATING APPARATUS Original Filed Jan.6, 1961 2 Sheets-Sheet 1 00@ OOO INVENTORS: JOHN D. NESBITT.

' E' 2 BY HERBERT M. KOHN. X &ame ak %GM p 1965 J. D. NESBITT ETAL3,208,740

HEATING APPARATUS 2. Sheets-Sheet 2 Original Filed Jan. 6, 1961INVENTORS: JOHN D.NESB|TT. BY HERBERT M. KOHN.

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United States Patent O Toledo, Ohio, Toledo, Ohio,

This application is a division of our prior application Serial No.81,118, filed January 6, 1961, now U.S. Patent 3,116,9l5.

This invention relates to heating apparatus found to have particularutility in low temperature processing applications up to the 1200 F. to1400 F. range wherein temperature uniforrnity requirements areespecially severe as, for example, glass tempering lehrs. Because of thewell known fragility of glass and similar products and the necessity ofobtaining uniform heating of glass to avoid residual stresses andstrains, direct convection heating has been avoided. Normal practice hasbeen to utilize indirect radiant heating elements of the electrical orfuelfired type with or without the use of some aux'liary convectionheating. In the specific case of heat treating glass sheets supported ona moving conveyor, previous designs commonly employed electric heatingelements mounted on the lehr side walls. The inherent difficulty withthis type of heating is that the electric heating elements becomelocalized sources of heat, and the wall area between elements is muchcolder and presents a non-uniform temperature radiating area to theglass.

In cases where fuel fired radiant tubes have been used in heat treatingglass and similar fragile materials, the problem of obtainingtemperatures uniforrnity becomes more severe than in using electricheating elements. Not only is there a problem of cooler wall areasbetween tubes or heating elements, but there is also a problem ofnon-uniform heating along the length of the individual tubes. Thisproblem is greatly accentuated when it is necessary to locate the tubestransversely of the work, i.e., acrossthe width of the moving sheet sothat the temperature nonuniformity of the tubes is reflected from edgeto edge of the work.

Direct firing for heating glass and similar materials is usually avoidedeven though the products of combustion are not deleterious to the workbecause the individual burners produce hot spots which cause a greatertemperature non-uniformity than electric or fuel-fired radiant tubes.

It is, therefore, an object of the present invention to provide acombustion system enabling a high degree of turndown without affectingtemperature uniformity.

Another object of the invention is to provide a combustion systemcapable of producing a uniform source of radiant heat whilesimultaneously providing a means of limited convection heating.

The application of the ported tube-eXcess-air burner combination to lowtemperature processing equipment such as glass lehrs permits theproduction of a radiant wall having a temperature uniformity heretoforeunobtainable by other heating methods. The ported distribution tubes arearranged along the side walls of the chamber with ports located so as todischarge products of comi 3,208,74o Patented Sept. 28, 1965 bustion tothe side wall portions between the tubes. The flue products on the wallsurfaces between the tubes produces an overall temperature uniformityparticularly advantageous for critical processing. The relatively slowmovement of the thoroughly mixed combustion products moving oil thewalls adds a moderate convection heating effect which is better thanthat produced in the usual direct fired furnace because of the largeamounts of excess-air and the elimination of hot spots attendant withthe usual direct firing.

Other and more specific objects of the invention will be apparent fromthe following specification and accompany `ing drawings, wherein likenumbers are used throughout to identity like parts.

In the drawings:

FIG. 1 is a fragmentary horizontal sectional view ot a glass temperingfurnace;

FIG. 2 is a vertical sectional view taken along the line 2-2 of FIG. l;

FIG. 3 is a sectional view taken along FIG. 1', and

FIG. 4 is a sectional view taken along line 4-4 of FIG. 1.

Referring now to FIG. l, there is shown a representative application ofthe invention for low temperature processing in the form of a typicalsection of a multiple section tempering lehr 53 of the vertical typewherein a glass sheet 54 moves therethrough in the direction of thearrow. More particularly, the glass sheet 54 is maintained in a verticalposition by a suitable device, such as an overhead conveyor (not shown),located eXteriorly of the furnace 53, or the glass sheet may be conveyedthrough the furnace on rollers 78, as shown in FIG. 2, assisted by guidemeans (not shown). A portion of this conveyor extends through a suitableslot (not shown) in the top of the furnace 53 to engage the glass sheet54.

The urnace or lehr 53 comprises a plurality of similar sections, each ofwhich has a front wall 55 and a similarly contoured rear wall 56 spacedtherefrom as shown in FIG. 1 with a bottom wall 57 and a top wall 58 asshown in FIG. 2. Two pairs of end walls 59 eXtend from the front wall 55and the rear wall 56 toward the center as shown in FIG. l. The end walls59 divide the furnace 53 into a plurality of zones, and a suitableopening isprovided between each pair of end walls 59 to enable the glasssheets 54 to be moved from one zone to another. Each successive Zone hasa temperature that is higher than the preceding Zone so that the glasssheets 54 are heated progressively to the proper temperature fortempering. Thus adjacent zones are in open communication with oneanother but are maintained at diiferent temperatures. Flues 60 areprovided in the wall 55 and rear wall 56 to remove the products ofcombustion from the furnace 53, and each flue is connected to an eXhaustfan (not shown).

According to the present invention, four vertical rows of horizontallydisposed tubes 61 are mounted within each section of the furnace 53 tworows being located adjacent the front wall 55 and the other two rowsbeing located adjacent the back wall 56 as shown in FIGS. 1 and 2. Thecombustion tubes 61 are connected to a plurality of burners 22 (FIG. 1)mounted eXteriorly of the furnace 53. Each of the burners 22 is of theeXcess air type and the preferred burner embodiment is shown in FIG. 4.Comline 3-3 of is uniformly heated U bustion air is supplied through aline (not shown) to the burner air inlet 35 at a substantially constantrate while a stream of fuel is supplied through a conduit 31.

As can be seen in FIG. 1, each of the combustion tubes 61 includes asubstantially straight, elongated portion 65 that is connected to one ofthe burners 22 through a curved portion or elbow 66 that is in fluidcommunication with both the burner 22 and the straight portion 65. Moreparticularly, each straight portion 65 has a flange 67 that is securedto a mating flange 68 on the curved portion 66 by any suitable manner.Each of the curved portions 66 is connected to its respective burner 22by a substantially straight neck section 69 that is located within aconical shaped passage 70 in the wall 55.

Each of the tubes 61 is supported by a pair of brackets 71 which areSecured to the inside surfaces of the front wall 55, and rear wall 56.As shown in FIG. 2, each pair of brackets 71 preferably mounts two tubes61 on the furnace 53. The directions in which the straight portions 65extend are staggered as shown in FIG. 2 to balance any temperaturegradients that might exist along the tubes 61.

Each straight portion 65 has a plurality of outlets or ports 72 incommunication with the interior of the furnace 53, and the products ofcombustion from each burner 62 which move through the curved portion 66and the straight portion 65 are introduced into the furnace 53 throughthe ports 72. As shown in FIG. 3, the ports 72 are positioned on theside of the straight portion 65 that is toward the lehr wall and theports 72 extend radially outwardly through the walls of each combustiontube 61 at an angle of approximately 45 degrees from a plane extendingthrough the center of the tube normal to the lehr wall. Thus, the hotproducts of combustion are directed toward the inner surface of the lehrwall to heat the same uniformly between combustion tubes 61, and walland tubes become a source of uniform radiant heat. The hot gases whichare deflected away from the walls become a source of moderate convectionheating.

The eXcess-air burner of FIG. 4 used to supply products of combustion tothe lehr of FIGS. 1 and 2 is similar in Construction and operation tothe eXcess-air burner described in the parent application to thisapplication, now issued as U.S. Patent 3,116,915 and, more particularly,the burner of FIG. 3 of the patent which is used to supply products ofcombustion to the make-up air heater of FIGS. 1, 2 and 4 of the patent.The primary difference between the burner of FIG. 4 of the applicationand the burner shown in FIG. 3 of U.S. Patent 3,1l6,9l5 is that thesleeve 77 and associated slots 78 of the patented burner have beeneliminated in the burner shown in FIG. 4 of the present application, andan apertured plate 36 has been substtuted. Plate 36 is placed on thedownstream end of cylindrical wall portion 30 and is provided with aplurality of spaced, axially extending passages 73 into the annular airchamber. These passages provide an aXial flow of cool air adjacent theinside diameter of the flue products distribution tube 23 which enclosesthe burning air-fuel mixture and reduces to a marked degree the tendencyof the elbow 66 downstream of the burner to overheat. Elbow sections areparticularly vulnerable to overheating because of the abrupt change indirection of the burning air-fuel mixture which causes additonal miXingand faster burning at that point. The provision of this novel cool airblanket is considered a novel improvement over the art and is readilyadaptable to many diflerent types of burners employed in a criticalheating process.

By using an eXcess-air type burner in the tempering furnace 53, asubstantially constant Volume of gas is emitted from each burner 22 evenduring turndown when no heat is required, because the flow of air ineach line 35 is kept constant. Not only is the temperature of thevarious tubes maintained quite uniform, but also each tube from end toend. While various sizes and spacings may be used for the outlets 72,those outlets must be angularly directed toward the wall 55 for properheating. The greater the number of outlets used, the more uniform willbe the heat distribution. The total flow of air within each Zone ismaintained both high and constant which is important where adjacentzones are in open communication with each other, as shown in FIG. 1, andparticularly when such Zones are controlled at diflerent temperatures.

While the preferred embodiment of the invention has been disclosed,various modifications can be made to the tube and excess air burnerwithout departing from the spirit of the invention or the scope of thesubjoined claims.

We claim:

1. In a glass tempering lehr of the type having oppositely disposed sidewalls and means for conveying glass sheets therethrough in a verticalposition, the improvement comprising; a plurality of burners mountedexterior of the furnace, combustion air supply means for delivering astream of combustion air to each of said burners at a substantiallyconstant rate, fuel supply means for delivering a stream of fuel to eachof said burners, and a plurality of combustion tubes mounted within thefurnace between the path of movement of the glass sheets and the sidewalls, each of said tubes having a substantially straight portionextending parallel to the path of movement of the glass sheets and acurved portion in fluid communication with one of said burners, saidsubstantially straight portion having a plurality of outlets in fluidcommunication With the interier of the furnace whereby products ofcombustion from said burner are transferred through said curved portioninto the furnace through said plurality of outlets.

2. Apparatus according to claim 1 wherein said plurality of said outletsare directed toward said side walls whereby the side walls andcombustion tubes become a source of substantially uniform radiant heatand products of combustion are deflected away from the side walls tobecome a source of convection heating.

3. In a longitudinally extending furnace having wall means forming awork chamber and means for conveying work to be treated therethrough ina predetermined path within said chamber, the improvement comprising: aplurality of nozzle mixing excess air burners mounted exteriorly of saidchamber; combustion air supply means for delivering a stream of air toeach of said burners at a substantially constant rate; fuel supply meansfor delivering a stream of fuel to each of said burners; and a pluralityof combustion tubes mounted within said chamber between saidpredetermined path and at least a portion of said wall means which islocated parallel to said predetermined path, each of said combustiontubes having first portion extending substantially parallel with saidportion of said wall means and a connecting portion in fluidcommunication with one of said burners, said first portion having aplurality of outlets directed toward said portion of said wall meanswhereby products of combustion are distributed through said combustiontubes and outlets therein and impinge against said portion of said wallmeans whereby said portion of the wall means and the combustion tubesbecome a source of substantially uniform radiant heat, and products ofcombustion are deflected away from said portion of said wall means tobecome a source of moderate convection heating.

4. In a longitudinally extending furnace having oppositely disposedsubstantially parallel side walls and means for conveying work to betreated therethrough in a predetermined path between said side walls,the improvement comprising: a plurality of nozzle mixing excess airburners mounted exteriorly of the furnace; combustion air supply meansfor delivering a stream of air to each of said burners at asubstantially constant rate; fuel supply means for delivering a streamof fuel to each of said burners;

and a plurality of combustion tubes mounted within the furnace betweensaid predetermined path and said side walls, each of said combustiontubes having a first portion extending substantially parallel with saidside walls and a connecting portion in fluid communication with one ofsaid burners, said first portion having a plurality of outlets directedtoward an adjacent side wall Whereby products of combustion aredistributed through said combustion tubes and outlets therein andimpinge against said side walls Whereby the side walls and combustiontubes become a source of substantially uniform radiant heat, andproducts of combustion are deflected away from the side walls to becomea source of convection heating.

References Cited by the Examiner UNITED STATES PATENTS 1,380,102 5/21Horn 263-6 1,574,839 3/26 Morse 126-91 2,486,018 10/49 Furkert 158-73,100,632 8/63 Mohrng 126-91 FOREIGN PATENTS 5 72,036 5 34 France.

CHARLES SUKALO, Pr'mary Examine'.

JOHN J. CAMBY, Examiner.

1. IN A GLASS TEMPERING LEHR OF THE TYPE HAVING OPPOSITELY DISPOSED SIDEWALLS AND MEANS FOR CONVEYING GLASS SHEETS THERETHROUGH IN A VERTICALPOSITION, THE IMPROVEMENT COMPRISING; A PLURALITY OF BURNERS MOUNTEDEXTERIOR OF THE FURNACE, COMBUSTION AIR SUPPLY MEANS FOR DELIVERY ASTREAM OF COMBUSTION AIR TO EACH OF SAID BURNERS AT A SUBSTANTIALLYCONSTANT RATE, FUEL SUPPLY MEANS FOR DELIVERING A STREAM OF FUEL TO EACHOF SAID BURNERS, AND A PLURALITY OF COMBUSTION TUBES MOUNTED WITHIN THEFURANCE BETWEEN THE PATH OF MOVEMENT OF THE GLASS SHEETS AND THE SIDEWALLS, EACH OF SAID TUBES HAVING A SUBSTANTIALLY STRIAGHT PORTINGEXTENDING PARALLEL TO THE PATH OF MOVEMENT OF THE GLASS SHEETS AND ACURVED PORTION IN FLUID COMMUNICATION WITH ONE OF SAID BURNERS, SAIDSUBSTANTIALLY STRAIGHT PORTION HAVING A PLURALITY OF OUTLETS IN FLUIDSCOMMUNICATION WITH THE INTERIOR OF THE FURNACE WHEREBY PRODUCTS OFCOMBUSTION FROM SAID BURNER ARE TRANSFERRED THROUGH SAID CURVED PORTIONINTO THE FURNACE THROUGH SAID PLURALITY OF OUTLETS.